The present disclosure relates to a data storage device. More particularly, the disclosure relates to a data storage device incorporating ballistic or quasi-ballistic electron emitters.
Researchers have continually attempted to increase the storage density and reduce the cost of data storage devices such as magnetic hard-drives, optical drives, and dynamic random access memory (DRAM). It has, however, become increasingly difficult to increase storage density due to fundamental limits such as the superparamagnetic limit, below which magnetic bits are unstable at room temperature.
Several approaches have been used to increase storage density of storage devices. One approach is based on scanned probe microscopy (SPM) technology. In such an approach, a probe is positioned extremely close to a storage medium. An example is atomic force microscopy (AFM) in which a probe is placed into physical contact with the storage medium. Another example is scanning tunneling microscopy (STM) in which the probe is placed within a few nanometers from the storage medium to ensure that the probe is within a tunneling range of the medium. Although limited success has been achieved through these approaches, it is difficult to inexpensively build a storage device having probes that contact or are in close proximity to the storage medium without eventually damaging the probe and/or the surface of the medium. Moreover, in STM, the spacing must be precisely controlled. As known by persons having ordinary skill in the art, such control is difficult to achieve.
In view of the difficulties associated with SPM, other researchers have developed methods that eliminate the need for extremely close proximity. One such technique is based on near-field scanning optical microscopy (NSOM). Although avoiding the proximity problem, this technique has limited lateral resolution and bandwidth and therefore is of limited applicability. Other techniques have been developed based on non-contact SFM, but these techniques typically suffer from poor resolution and poor signal to noise ratio.
Even where increased storage density can be achieved, hurdles to effective implementation exist. Once such hurdle is the time required to access data stored on the storage device the information. Specifically, the utility of the storage device is limited if a long time is required to retrieve the stored data. Therefore, in addition to high storage density, there must be a way to quickly access the data.
Recently, semiconductor-based electron sources have been developed that can be used in storage devices and which may avoid the difficulties noted above. An example of such a data storage device is described in U.S. Pat. No. 5,557,596. The device described in that patent includes multiple electron sources having electron emission surfaces that face a storage medium. During write operations, the electron sources bombard the storage medium with relatively high intensity electron beams. During read operations, the electron sources bombard the storage medium with relatively low intensity electron beams. Such a device provides advantageous results. For instance, the size of storage bits in such devices may be reduced by decreasing the electron beam diameter, thereby increasing storage density and capacity and decreasing storage cost.
One type of electron source described in the U.S. Pat. No. 5,557,596 is the xe2x80x9cSpindtxe2x80x9d emitter. As described in the patent, such an emitter has a cone shape that ends in a tip from which electron beams can be emitted. Typically, the tip is made as sharp as possible to reduce operating voltage and achieve a highly focused electron beam diameter. Unfortunately, utilization of Spindt emitters creates other problems. First, the fabrication of sharp emitter tips is difficult and expensive. In addition, focusing the electron beam from a Spindt tip in a temporally and spatially stable manner is difficult. Furthermore, the electron optics that provide the focusing can become complicated. Moreover, Spindt emitters do not operate well in poor vacuums. These problems become especially prominent as the electron beam diameter is reduced below 100 nanometers.
From the foregoing, it can be appreciated that it would be desirable to have a data storage device that employs electron emitters but that avoids one or more of the problems identified above.
The present disclosure relates to a data storage device, comprising a plurality of electron emitters adapted to emit electron beams, the electron emitters each having a planar emission surface, and a storage medium in proximity to the electron emitter, the storage medium having a plurality of storage areas that are capable of at least two distinct states that represent data, the state of the storage areas being changeable in response to bombardment by an electron beams emitted by the electron emitters, wherein data is written to the device by changing the state of the storage areas and data is read by the device by observing phenomena relevant to the storage areas.
In addition, the disclosure relates to a method for storing data, comprising the steps of emitting an electron beam from an electron emitter including a planar emission surface, directing the electron beam toward a storage medium comprising a plurality of storage areas, and bombarding one of the storage areas with electrons with the electron beam so as to change the state of a storage area. Typically, although not necessarily, the method further comprises the step of bombarding one of the storage areas with electrons with a lower current electron beam and observing its effect on the storage area.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.